Abstracts

Rationale: Epileptic encephalopathies (EE) are severe childhood epilepsy syndromes characterized by multiple refractory seizure types, developmental arrest or regression and a poor prognosis. In most cases, the cause is unknown, but de novo genetic mutations have been identified in some patients. We recently performed exome sequencing in 264 probands and their unaffected parents for two classic EE syndromes: infantile spasms (IS; n=149) and Lennox Gastaut syndrome (LGS; n=115). We confirmed 329 de novo mutations in 309 genes and found an excess of de novo mutations in the ~4000 genes that are most intolerant to functional genetic variation in the human population (Epi4k & EPGP Investigators, 2013, Nature). Notably, we identified four patients with de novo mutations in GABRB3 and two patients with the identical de novo mutation in ALG13, confirming these two genes as novel EE genes. While many of the other genes in which there were de novo mutations are reasonable candidate genes for EE, identification of additional patients with mutations is necessary to confirm the role of each gene in the genetic etiology of EE. Methods: Here, we perform targeted capture and high-throughput resequencing of 31 genes in which a de novo mutation was identified in one or more patients with IS or LGS in our prior study. We selected genes in which two unrelated probands had a de novo mutation (n=4, including GABRB3 and ALG13), genes that are among those intolerant to genetic variation and in which the de novo mutation was severe (nonsense, frameshift, splice; n=8), and genes in which mutations have previously been reported in other epilepsy syndromes, brain malformation syndromes, intellectual disability, autism or related phenotypes (n=19). We are screening ~600 patients with a range of EE syndromes, as we anticipate that many of the genes will cause EE disorders other than IS or LGS. Results: We will report the frequency of de novo mutations of each candidate gene in our cohort and investigate genotype-phenotype correlations for each gene in which multiple patients harbor mutations.Conclusions: High-throughput mutation screening of candidate genes in a large cohort of patients with EE will facilitate disease gene validation and genotype-phenotype studies.